There is a crucial difference between Caterham and Marussia's situation. The F1 entry (and Concorde agreement signatory) is 1MRT, a company based in Malaysia. This company is not insolvent whereas their supplier company is. This means that Caterham's F1 entry - if they miss only two races - is still valid. Marussia's however is in a trickier position as the company with the F1 entry has gone into administration which in theory means it loses it's F1 entry as it is insolvent. So in theory Marussia cannot come back, wether they miss one race, two races or more - because they are in administration they forfeit their F1 entry. Maybe someone will buy Caterham's entrant (1MRT) from who ever owns that at the moment, and then purchase the remnants of the Marussia facilities but as individual entities... I think that is no longer an option...
I don't think that is quite right. Marussia has entered into voluntary administration but the company has not been wound up. If (and it is a big if, I know) the Administrator is able to find a buyer for Marussia as a going concern and they only miss one or two races, the company's F1 entry remains valid. The situation with Caterham is more complicated precisely because of the split between the F1 entry holding company and the company running (and owning?) the cars.Even if the Administrator is able to find a buyer for Caterham, the buyer will have to do a deal with the entry holder to continue racing. Equally, the entry holder would have to conjure up some F1 cars if it wanted to continue separately from Caterham. The fact that there is still uncertainty over who currently owns Caterham just adds to the problems.
Realistcally, I doubt very much that we will see either Caterham or Marussia again - they seem fated to join the long and depressing list of plucky but extinct F1 minnows and dead ducks.